Gel electrophoresis is a powerful tool for separating, identifying, and purifying DNA fragments. Molecular information obtainable by this technique is directly attributable to intrinsic properties of the individual DNA fragments. Although indespensible for preparative work, which requires a physical separation of the fragments, the use of gel electrophoresisfor analysis of fragment size distributions is inefficient. The technique is inherently time consuming, requiring net migrations through a gel over a period of hours. However, the intrinsic properties of DNA fragments affecting net migration rates also affect mobilities associated with rotational diffusion rates. Therefore a measure of the rotational diffusion rate, or relaxation time, will provide the same characteristic fragment information as gel electrophoresis. Since a physical separation is not required, analysis could be accomplished in a considerably shorter period of time. BiPhotonics Corporation proposes to develop an instrument capable of analyzing unseparated and unstained DNA fragments in a gel matrix. By measuring the optical birefringence response to a swept frequency electric field, analysis of characteristic relaxation frequencies will provide the necessary mobility, and thus molecular weight information, for determining the distribution of fragment lengths within a DNA sample.